Interpretive Summary: An H7N3 highly pathogenic avian influenza (HPAI) outbreak in poultry has been recently reported in the State of Jalisco (Mexico). In order to evaluate which vaccination program may be optimal against such AI virus (AIV) infection, we vaccinated egg-producing chickens with a technologically advanced fowlpox virus vaccine with an influenza gene insert (rFPV-H7-AIV) and a killed inactivated AIV vaccine, and subsequently challenged against the Jalisco HPAIV. All vaccine combinations provided similar and significant protection against disease, mortality, and virus growth. Control of the recent Jalisco AIV infection could be achieved by a single dose of rFPV-H7-AIV vaccine at 1-day-of-age, although optimal protection may require a second dose of killed vaccine administered in the field.

Technical Abstract:
Beginning on June 2012, an H7N3 highly pathogenic avian influenza (HPAI) epizootic was reported in the State of Jalisco (Mexico), with some 22.4 million chickens that died, were slaughtered on affected farms or were preemptively culled on neighboring farms. In the current study, layer chickens were vaccinated with a recombinant fowlpox virus vaccine containing a low pathogenic AI (LPAI) H7 gene insert (rFPV-H7-AIV) and an inactivated oil-emulsified H7N3 AIV vaccine, and subsequently challenged against the Jalisco H7N3 HPAIV. All vaccine combinations provided similar and significant protection against mortality, morbidity, and shedding of challenge virus from the respiratory and gastrointestinal tracts. Serological data also suggested analogous protection from HPAIV among immunized birds. Control of the recent Jalisco AIV infection could be achieved by using various combinations of the two vaccines tested. Even though a single dose of rFPV-H7-AIV vaccine at 1-day-of-age would be the most pragmatic option, optimal protection may require a second dose of vaccine administered in the field.